Method of treatment of dredged material for beneficial use

ABSTRACT

A method for the decontamination and solidification of dredged material is described. The method includes, in the following order, (a) adding a lime-based binder to dredged material to form a mixture; (b) letting the mixture cool to about ambient temperature; and (c) adding to the mixture a chelating agent. The order of the steps may not be reversed without affecting the effectiveness of the treatment of the dredged material. A method for producing filler containing decontaminated and solidified dredged material is also described. The method includes treating dredged material with a lime-based binder and a chelating agent and adding the resulting mixture to concrete.

SPECIFICATION

[0001] This application claims priority to U.S. Provisional ApplicationNo. 60/276,445, filed Mar. 16, 2001, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention is directed to a method for the treatment ofdredged material. More particularly, this invention is directed to amethod to decontaminate and solidify dredged material so as to render itsuitable for beneficial use.

[0004] 2. Background Information

[0005] Harbors and waterways require shipping lanes to be dredged on aregular maintenance basis in order to prevent the shipping lanes fromsilting up. Material that is dredged out of port or harbor locationstypically contains a wide range of toxic contaminants, from heavy metalsto oils and pesticides. Three alternatives may be considered formanagement of dredged material: confined disposal, open-water disposal,and beneficial use.

[0006] Confined disposal is problematic since confined facilities musthave all potential escape routes of the contaminants eliminated,including effluents during placement, surface runoff, leachates, directuptake by plants and animals and volatilization to air. Open-waterdisposal is limited by the fact that the dumping of contaminatedsediments in waters is not permitted under various legislative measures,including, for example, the Marine Protection, Research, and SanctuariesAct. Accordingly, treatment of the contaminated dredged material forrendering it suitable for beneficial use is a most desirablealternative.

[0007] Several examples of beneficial use are available. For example,the dredged material may be used as beach nourishment, which may benecessary if natural replacement of material moved along the shorelineby littoral transport is not available. However, only the gravel andsand portion of dredged material is suitable for beach nourishment,making separation and decontamination obligatory. As a second example,dredged material may be used as manufactured topsoil; however, only fineparticles are suitable for such use, so that separation anddecontamination of clay and silt is required. In addition, when used foragricultural purposes, the material has to be suitably clean and mustnot contain excessive amounts of salts, which can make the materialunusable for growth of most plants. A more promising beneficial use fordredged material is as a filler for composite materials. However, suchuse requires not only effective decontamination but also solidificationof the dredged material.

[0008] One solution to the problem of treatment of contaminated dredgedmaterial is the use of chemical substances capable of neutralizing heavymetals and other toxins, such as the chelating agents described in U.S.Pat. No. 5,714,085 (herein incorporated by reference). For example, thechelating agents of U.S. Pat. No. 5,714,085 remove heavy metals andcertain organic contaminants such as polychlorinated biphenyls. Thesechelating agents are advantageous when compared to microorganisms, whichcan remove organic contaminants but cannot remove heavy metals and otherinorganic contaminants. However, the chelating agents of U.S. Pat. No.5,714,085 were developed only for decontamination, and not forsolidification as well. Solidification of the dredged material isnecessary to make it suitable as a filler for composite materials suchas concrete.

[0009] None of the prior art, including U.S. Pat. No. 5,714,085,provides a commercially viable method that results both indecontamination and in solidification of the dredged material thatrenders the material suitable as a filler for composite materials.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the invention to provide a methodfor the treatment of dredged material, where the method comprises, inthe following order: adding to dredged material a lime-based binder toform a mixture; letting the mixture cool to about room temperature; andadding a chelating agent. This method results in decontamination andsolidification of the dredged material and renders the material suitableas a filler for composite materials. The sequential steps of adding alime based binder and then adding a chelating agent exhibit anunexpected synergistic effect in decontaminating the dredged materialwhile solidifying the material.

[0011] A further object of the invention is to provide a method suitablefor the treatment of both dry and wet dredged material.

[0012] A further object of the invention is to provide a method for theproduction of a filler containing dredged material treated first with alime-based binder and then with a chelating agent.

[0013] One advantage of the method of the invention is that it providesa highly decontaminated solidified dredged material which makes itsuitable for use as a filler for composite materials such as concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 shows the particle size distribution of natural dry dredgedmaterial (“NYH dry” in FIG. 1) and of dredged material after combinedtreatment with a lime-based binder and a chelating agent (“DMCJ” in FIG.1).

[0015]FIG. 2 shows the cumulative particle size distribution of naturaldry dredged material (NYH dry) and of dredged material after treatmentwith a lime-based binder and a chelating agent (DMCJ).

[0016]FIG. 3 shows an optical microscope observation of dry dredgedmaterial at 100× magnification.

[0017]FIG. 4 shows an optical microscope observation of dry dredgedmaterial after treatment with a lime-based binder and a chelating agentat 100× magnification. The arrows mark agglomerates around oil products.

[0018]FIG. 5 shows plots of compressive strength versus dredged material(“DM” in FIG. 5) content after 7 and 28 days.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The method of the present invention includes at least twoseparate steps carried out in sequence. The first of the two stepsincludes solidification of dredged material by treatment with alime-based binder. In one exemplary embodiment, the binder is apulverized quick-lime, such as CAL-MAX pulverized fine quick-limeavailable from Ash Grove Cement Co. Preferably, the pulverizedquick-lime comprises at least 80% by weight of active calcium oxide, upto 1% by weight of magnesium oxide, up to 2% by weight of silica, up to0.2% by weight of ferric oxide, and up to 0.2% by weight of aluminumoxide. Most preferably, the mean diameter of the particles of thepulverized quick-lime is about 45 μm (325 mesh). All of the quicklimematerial passed a no. 30 sieve. The phrase “active calcium oxide” isintended to mean calcium oxide that is capable of readily reacting withwater at ambient temperature. The term “ambient temperature” as usedherein refers to the atmospheric temperature at the location wheretreatment of the dredged material takes place. Once calcium oxide hasreacted with water, it is no longer “active calcium oxide.”

[0020] The hydration of the pulverized quick-lime results in raising thetemperature of the mixture to about 212° F. and greatly reduces thewater content and therefore the volume of the raw dredged material. Thistreatment solidifies the dredged material. After the dredged materialhas cooled to ambient temperature, it is suitable for furtherprocessing, either dried or wet. The term cooling is intended to referto natural or passive cooling, rather than forced or active cooling.

[0021] The lime-based binder treatment changes the structure and textureof the dredged material. While the untreated material partly consists ofclay-sand agglomerates with closed structure and similar particle sizedistribution as regular, but fine sand aggregate, after the lime-basedbinder treatment it exhibits a very fine, porous structure nearlywithout conglomeration. The particles are separated from each other, andif they are bound by the hydrated lime-based binder, these bonds can bebroken with relative ease.

[0022] The lime-based binder treatment also changes the surfaceproperties of the dredged material. The surface charge is altered,making the surface accessible to polar or charged substances such aswater or superplasticizers. As side benefits, increased homogeneity andless saline material on the surface were observed. The odor diminished,which is an indication that volatile organics are either destroyed orbound.

[0023] The lime-based binder, in addition to causing dehydration andsolidification, also causes a rise in the pH-level, which creates thebasis for very effective decontamination of the dredged material.

[0024] The second of the two steps of the method of the presentinvention, which is subsequent to the first step, includes treatment ofthe dredged material with a chelating agent. Preferably, the chelatingagent is capable of chelation of and formation of coordination compoundswith chemical contaminants in the dredged material. For example, whenthe contaminant is a metal M, the chelating agent is capable ofproviding one or more coordinating moieties X which encapsulate themetal M to form a coordination compound comprising the structural unitM(X)_(n), where n is the number of moieties X that coordinate the metalcenter. The number n depends on the nature of the metal. Such achelating agent has the capability of encapsulation of pollutants, suchas heavy metals and polychloride biphenyls (PCB). The treatment isrelatively fast, reliable, and effective.

[0025] In one particularly advantageous exemplary embodiment of theinvention, the chelating agent is one of the chelating agents describedin U.S. Pat. No. 5,714,085, which can remove contaminants such as heavymetals and PCB. The compositions of two exemplary chelating agents inthe form of solutions are described in Table 1: TABLE 1 Chemicalcomposition of exemplary solutions of chelating agents Concentration,g/liter Ingredient Chelating agent A Chelating agent B Sodium chloride44 83 Potassium chloride 87 125.3 Potassium bromide 6 9 Calcium sulfate8 12 Lithium chloride 1.7 2.4 Barium chloride 12 18 Magnesium chloride 812 Strontium chloride 4 6 Cobalt chloride 8 12 Zinc chloride 3 6 Copperchloride 3 6 Tannin 11 11.6 Pyrolignous acid Saturated solutionSaturated solution

[0026] Chelating agents A and B were used separately to treat thedredged material. In one advantageous embodiment of the invention, thechelating agent is present in an amount of about 3% to about 10% byweight of the dredged material. The effectiveness of each of agents Aand B was evaluated in terms of the degree of efflorescence of thechlorides of sodium, potassium, and other metals. Agent A was shown tobe more effective than agent B: samples containing agent B showedintensive efflorescence of sodium, potassium and other chlorides, whilesamples containing agent A showed much lower efflorescence levels. It isbelieved that the ability of a chelating agent in removing metals suchas sodium or potassium is a qualitative measure of its ability todecontaminate heavy metals. Accordingly, agent A is preferable as thechelating agent for the dredged material treatment described herein.

[0027] Treatment with a chelating agent alone does not seem to be asufficient preparation of dredged material for further beneficial usebecause chelating agents generally provide for decontamination only. Wehave discovered that by first treating the dredged material with alime-based binder and then treating the mixture of the dredged materialand the lime-based binder with a chelating agent, one obtainsdecontamination of the dredged material to an extent greater than theeffect of the chelating agent when used alone.

[0028] In accordance with the present invention, the order of the twosteps described above, i.e. addition of a lime-based binder andsubsequent addition of a chelating agent, may not be reversed withoutsignificantly reducing the effectiveness of the decontamination andsolidification.

[0029] The combined treatment of the present invention causes a shift tofiner particle sizes, as illustrated in FIGS. 1 and 2. This shiftindicates that the surface structure is altered and that conglomerates,especially around oil products, are either destroyed or spread out. Inthe material after treatment, the agglomerates of oil products are verysmall as compared to the untreated dredged material, as evidenced inFIGS. 3 and 4, which show microscope observations at ×100 magnificationof the dredged material before treatment and after the combinedtreatment of the present invention, respectively.

[0030] To study the effectiveness of the combined treatment of thepresent invention, dredged materials were subjected to a leaching testfollowing the Environmental Protection Agency Toxicity CharacteristicLeaching Procedure as described in Federal Register Vol. 51, No. 216,November 1986, Rules and Regulations. Three samples were analyzed: anuntreated reference sample (raw dredged material), a sample treated onlywith chelating agent A, and a sample which had undergone the combinedtreatment of the present invention. The results of the test aresummarized in Table 2. TABLE 2 Results of chemical analysis (values arein ppm of dry material) Dredged material Dredged Natural treatedmaterial treated Dredged with chelating with lime-based binder SubstanceMaterial (‘DM’) agent A and chelating agent A Leachable 0.27 ND* (<0.1)ND (<0.1) Cyanide Cadmium 0.22 0.20 ND (<0.02) Lead 0.38 0.53 0.17

[0031] As can be seen from Table 2, the data exhibit the effectivenessof the combined treatment. The treatment with only chelating agent A isineffective in reducing the amount of heavy metals detectable in aleaching test—in fact, a larger fraction of lead present in the dredgedmaterial leached out than in the untreated sample. In contrast, thecombined treatment of the present invention considerably reduces bothleachable cyanide and heavy metals.

[0032] The treated dredged material of the present invention may be usedas a filler for concrete or mortar compositions. In order to evaluatethe viability of the method of the present invention, properties of bothfresh and hardened concrete obtained with both untreated and treateddredged material were tested. The behavior of concrete when mixed withuntreated dredged material provides reference data, which can be used toassess the effectiveness of treatment procedures.

[0033] The treatment of the dredged material includes the followingsteps. The dredged material and the lime-based binder are mixed.Preferably, the lime-based binder is in the amount ranging from about 3%to about 75% by weight of the dredged material. The hydration of thelime-based binder is accompanied by generation of heat and reduces thewater content of the dredged material drastically. A solid mixture isformed which is allowed to cool down to about ambient temperature and isthen mixed with a chelating agent, preferably chelating agent Adescribed above, to form a new mixture. The water content of thechelating agent solution hydrates the lime-based binder, so that the newmixture remains solid. The new mixture may be placed in a rotary dryerto form chips, or in a granulator to form granules. The chips, granules,or combination thereof were dried to a sufficient hardness and ground ina ball mill to produce a filler comprising particles, preferably ofabout 10 to about 150 μm in diameter, of decontaminated and solidifieddredged material. In one exemplary embodiment of the invention, thedrying period is less than or equal to two weeks.

[0034] The filler is particularly suitable as an additive to a compositematerial if it is pulverized, preferably to a particle size of about 10to about 150 μm in diameter. In one embodiment of the invention, thecomposite material is concrete. Preferably, the composite material isselected from the group consisting of cement-based concrete and polymerconcrete. In another embodiment of the invention, the composite materialis selected from the group consisting of cement, a mixture ofcementitious materials, a mixture of cementitious materials and sand, amixture of cementitious materials and gravel aggregate, or anycombination thereof.

[0035] Prior mixing of cement and the chelating agent does not stronglyaffect the concrete or mortar properties. In contrast, in the preferredmixing procedure, the chelating agent is administered to the mixcontaining the lime-based binder after the drying and cooling-offperiod, which leads to an unexpectedly large decrease in leachablecontaminants from the concrete containing dredged material.

[0036] Leaching tests were conducted on mortar samples containing 20%dredged material. The results of the leaching tests are shown in Table3. Referring to Table 3, Sample 23 contained untreated dredged material,sample 24 was treated with chelating agent A, and samples 21 and 22 weretreated with two variations of the combined treatment, i.e. first addingthe lime-based binder, and then adding the chelating agent before orafter the mixture of the dredged material and the lime-based binder hascooled to about ambient temperature. TABLE 3 Results of chemicalanalysis of mortar samples (in ppm) Sample #23 Sample #24 Sample #22Sample #21 Prior dredged — Chelating Lime-based Lime-based materialagent A binder and binder and treatment chelating chelating agent Aagent A after cooling period Leachable 1.22 0.82 0.44 0.41 cyanideCadmium ND < 0.02 ND < 0.02 ND < 0.02 ND < 0.02 Lead ND < 0.01 ND < 0.01ND < 0.01 ND < 0.01

[0037] As can be seen from Table 3, both variations of the combinedtreatment in accordance with the present invention are more effective insubstantially reducing the amount of leachable cyanide than treatmentwith only chelating agent A or no treatment. The concentrations of heavymetals analyzed were too low to allow comparison among the four samples.

[0038] Without wishing to be bound by any theory or mechanism, it isbelieved that the superior decontamination effect of the combinedtreatment of the invention relative to the treatment with a chelatingagent alone is due to the deconglomeration of the dredged material upontreatment with lime-based binder. As discussed above, the dredgedmaterial after deconglomeration exhibits a very fine, porous structure.This structure is more effectively treatable by the chelating agent thanthe structure of dredged material which has not been treated withlime-based binder, as shown in Tables 2 and 3. The order in which thechelating agent and the lime-based binder are added is thereforecritical in enabling the method of the invention to achieve a level ofdecontamination which is superior to that obtained by treatment with thechelating agent alone, which does not decontaminate dredged materialeffectively, or with the lime based binder alone, which only solidifiesthe dredged material.

[0039] The effect of the filler on the strength of concrete or mortarcompositions was also investigated and is shown in Table 4. TABLE 4Mortar strength with filler comprising treated dredged material Filler,Type 7-Day 28-Day % in of Aggregate/ compressive compressive cementtreatment Cement ratio strength (MPa) strength (MPa) 0 None 2.25 21.133.0 45 None 2.25 23.3 29.6 45 Chelating 2.25 23.4 27.2 Agent A 45Lime-Based 2.25 26.6 38.6 Binder 45 Combined 2.25 22.2 35.9 45 None 3.023.3 29.1 45 Chelating 3.0 22.2 25.9 Agent A 45 Lime-Based 3.0 28.0 37.6Binder 45 Combined 3.0 23.1 37.3

[0040] Table 4 shows that the compressive strength of the mortarcontaining the filler obtained from the combined treatment of thepresent invention is comparable, and in some cases superior, to themortar strength obtained with no treatment or with treatment withchelating agent A alone. Thus, in addition to the benefit of providingsuperior decontamination as discussed in Table 3, the combined treatmentif the present invention also provides good strength characteristics.

[0041] Another method for the production of a composite material havingsolidified dredged material as a filler comprises as a first step addinguntreated dredged material to a composite material to form a mixture. Inone embodiment of the invention, the composite material is concrete. Inanother embodiment of the invention, the composite material is selectedfrom the group consisting of cement, a mixture of cementitiousmaterials, a mixture of cementitious materials and sand, a mixture ofcementitious materials and gravel aggregate, or any combination thereof.A lime-based binder and a chelating agent, preferably chelating agent A,are then added in this order to the mixture. The mixture is then allowedto cool to about ambient temperature.

[0042] It should be understood that various changes and modifications tothe preferred embodiments described herein will be apparent to thoseskilled in the art without departing from the spirit and scope of thisinvention, the scope being defined by the appended claims.

1. A method for the decontamination and solidification of dredgedmaterial, comprising, in the following order: (a) adding a lime-basedbinder to dredged material to form a mixture; (b) letting the mixturecool to about room temperature; and (c) adding to the mixture achelating agent.
 2. The method of claim 1, wherein the lime-based binderis pulverized quick-lime.
 3. The method of claim 2, wherein thepulverized quick-lime comprises quick-lime particles having a meandiameter of about 45 μm.
 4. The method of claim 2, wherein thepulverized quick-lime comprises active calcium oxide, magnesium oxide,silica, ferric oxide, and aluminum oxide.
 5. The method of claim 4,wherein the pulverized quick-lime comprises at least 80% by weight ofactive calcium oxide, up to 1% by weight of magnesium oxide, up to 2% byweight of silica, up to 0.2% by weight of ferric oxide, and up to 0.2%by weight of aluminum oxide.
 6. The method of claim 1, wherein thechelating agent is a chemical composition providing chelation of andformation of coordination compounds with chemical contaminants in thedredged material.
 7. The method of claim 6, wherein the chelating agentcomprises in solution sodium chloride, potassium chloride, potassiumbromide, calcium sulfate, lithium chloride, barium chloride, magnesiumchloride, strontium chloride, cobalt chloride, zinc chloride, copperchloride, tannin and pyrolignous acid.
 8. The method of claim 7, whereinthe chelating agent comprises in solution sodium chloride in aconcentration of about 44 g/liter, potassium chloride in a concentrationof about 87 g/liter, potassium bromide in a concentration of about 6g/liter, calcium sulfate in a concentration of about 8 g/liter, lithiumchloride in a concentration of about 1.7 g/liter, barium chloride in aconcentration of about 12 g/liter, magnesium chloride in a concentrationof about 8 g/liter, strontium chloride in a concentration of about 4g/liter, cobalt chloride in a concentration of about 8 g/liter, zincchloride in a concentration of about 3 g/liter, copper chloride in aconcentration of about 3 g/liter, tannin in a concentration of about 11g/liter, and pyrolignous acid in a concentration saturating thesolution.
 9. A method for producing a filler for a composite material,comprising, in the following order: (a) adding a lime-based binder todredged material to form a mixture; (b) letting the mixture cool toabout ambient temperature; (c) adding a chelating agent to form a newmixture; (d) forming from the new mixture at least one of chips,granules, and a combination thereof; (e) drying the at least one ofchips, granules, and a combination thereof formed in step (d); and (f)grinding in a ball mill the at least one of chips, granules, and acombination thereof dried in step (e) to form the filler, the drying andthe grinding being carried out at about ambient temperature.
 10. Themethod of claim 9, wherein after the grinding step the filler comprisesparticles of treated dredged material having a diameter of about 10 μmto about 150 μm.
 11. The method of claim 9, wherein the lime-basedbinder is added in the amount ranging from about 3% to about 75% byweight of the dredged material.
 12. The method of claim 9, wherein thefiller is used as an additive to a composite material.
 13. The method ofclaim 12, wherein the composite material is selected from the groupconsisting of cement, a mixture of cementitious materials, a mixture ofcementitious materials and sand, a mixture of cementitious materials andgravel aggregate, or any combination thereof.
 14. The method of claim12, wherein the composite material is concrete.
 15. The method of claim9, wherein the lime-based binder is pulverized quick-lime.
 16. Themethod of claim 15, wherein the pulverized quick-lime comprisesquick-lime particles having a mean diameter of about 45 μm.
 17. Themethod of claim 15, wherein the pulverized quick-lime comprises activecalcium oxide, magnesium oxide, silica, ferric oxide, and aluminumoxide.
 18. The method of claim 17, wherein the pulverized quick-limecomprises at least 80% by weight of active calcium oxide, up to 1% byweight of magnesium oxide, up to 2% by weight of silica, up to 0.2% byweight of ferric oxide, and up to 0.2% by weight of aluminum oxide. 19.The method of claim 9, wherein the chelating agent comprises a chemicalcomposition for chelation of and formation of coordination compoundswith chemical contaminants in the dredged material.
 20. The method ofclaim 19, wherein the chelating agent comprises in solution sodiumchloride, potassium chloride, potassium bromide, calcium sulfate,lithium chloride, barium chloride, magnesium chloride, strontiumchloride, cobalt chloride, zinc chloride, copper chloride, tannin andpyrolignous acid.
 21. The method of claim 20, wherein the chelatingagent comprises a solution comprising sodium chloride in a concentrationof about 44 g/liter, potassium chloride in a concentration of about 87g/liter, potassium bromide in a concentration of about 6 g/liter,calcium sulfate in a concentration of about 8 g/liter, lithium chloridein a concentration of about 1.7 g/liter, barium chloride in aconcentration of about 12 g/liter, magnesium chloride in a concentrationof about 8 g/liter, strontium chloride in a concentration of about 4g/liter, cobalt chloride in a concentration of about 8 g/liter, zincchloride in a concentration of about 3 g/liter, copper chloride in aconcentration of about 3 g/liter, tannin in a concentration of about 11g/liter, and pyrolignous acid in a concentration saturating thesolution.
 22. A method for producing a composite material comprisingsolidified dredged material, comprising, in the following order: (a)adding untreated dredged material to one of cement, a mixture ofcementitious materials, a mixture of cementitious materials and sand, amixture of cementitious materials and gravel aggregate, or anycombination thereof, to form a first mixture; (b) adding a lime-basedbinder to the first mixture formed in step (a) to form a second mixture;(c) adding a chelating agent to the second mixture formed in step (b) toform a third mixture; and (d) allowing the third mixture cool to aboutambient temperature.
 23. The method of claim 22, wherein the lime-basedbinder is a pulverized quick-lime.
 24. The method of claim 22, whereinthe chelating agent is a chemical composition for chelation of andformation of coordination compounds with chemical contaminants in thedredged material.
 25. A method for producing a composite materialcomprising solidified dredged material, comprising, in the followingorder: (a) adding untreated dredged material to one of cement, a mixtureof cementitious materials, a mixture of cementitious materials and sand,a mixture of cementitious materials and gravel aggregate, or anycombination thereof, to form a first mixture; (b) adding a lime-basedbinder to the first mixture formed in step (a) to form a second mixture;(c) allowing the second mixture formed in step (b) cool to about ambienttemperature; and (d) adding a chelating agent to the second mixture toform a third mixture.